Index: channels/chan_sip.c
===================================================================
--- channels/chan_sip.c	(revision 207316)
+++ channels/chan_sip.c	(working copy)
@@ -18617,8 +18617,13 @@
 	sipmethod = find_sip_method(msg);
 
 	owner = p->owner;
-	if (owner) 
+	if (owner) {
+		char causevar[256], causeval[256];
 		owner->hangupcause = hangup_sip2cause(resp);
+		snprintf(causevar, sizeof(causevar), "MASTER_CHANNEL(HASH(SIP_CAUSE,%s))", owner->name);
+		snprintf(causeval, sizeof(causeval), "SIP %s", REQ_OFFSET_TO_STR(req, rlPart2));
+		pbx_builtin_setvar_helper(owner, causevar, causeval);
+	}
 
 	/* Acknowledge whatever it is destined for */
 	if ((resp >= 100) && (resp <= 199)) {
Index: funcs/func_channel.c
===================================================================
--- funcs/func_channel.c	(revision 207316)
+++ funcs/func_channel.c	(working copy)
@@ -55,6 +55,15 @@
 			will be space-delimited.</para>
 		</description>
 	</function>
+	<function name="MASTER_CHANNEL" language="en_US">
+		<synopsis>
+			Gets or sets variables on the master channel
+		</synopsis>
+		<description>
+			<para>Allows access to the channel which created the current channel, if any.  If the channel is already
+			a master channel, then accesses local channel variables.</para>
+		</description>
+	</function>
 	<function name="CHANNEL" language="en_US">
 		<synopsis>
 			Gets/sets various pieces of information about the channel.
@@ -496,23 +505,49 @@
 	.read = func_channels_read,
 };
 
+static int func_mchan_read(struct ast_channel *chan, const char *function,
+			     char *data, struct ast_str **buf, ssize_t len)
+{
+	struct ast_channel *mchan = ast_channel_get_master(chan);
+	char *template = alloca(4 + strlen(data));
+	sprintf(template, "${%s}", data); /* SAFE */
+	ast_str_substitute_variables(buf, len, mchan ? mchan : chan, template);
+	return 0;
+}
+
+static int func_mchan_write(struct ast_channel *chan, const char *function,
+			      char *data, const char *value)
+{
+	struct ast_channel *mchan = ast_channel_get_master(chan);
+	pbx_builtin_setvar_helper(mchan ? mchan : chan, data, value);
+	return 0;
+}
+
+static struct ast_custom_function mchan_function = {
+	.name = "MASTER_CHANNEL",
+	.read2 = func_mchan_read,
+	.write = func_mchan_write,
+};
+
 static int unload_module(void)
 {
 	int res = 0;
-	
+
 	res |= ast_custom_function_unregister(&channel_function);
 	res |= ast_custom_function_unregister(&channels_function);
-	
+	res |= ast_custom_function_unregister(&mchan_function);
+
 	return res;
 }
 
 static int load_module(void)
 {
 	int res = 0;
-	
+
 	res |= ast_custom_function_register(&channel_function);
 	res |= ast_custom_function_register(&channels_function);
-	
+	res |= ast_custom_function_register(&mchan_function);
+
 	return res;
 }
 
Index: include/asterisk/channel.h
===================================================================
--- include/asterisk/channel.h	(revision 207316)
+++ include/asterisk/channel.h	(working copy)
@@ -2640,6 +2640,14 @@
  * 	'0'
  */
 int ast_channel_connected_line_macro(struct ast_channel *autoservice_chan, struct ast_channel *macro_chan, const void *connected_info, int caller, int frame);
+
+/*!\since 1.6.3
+ * \brief Retrieve a channel pointer for the channel which created this one, if any.
+ * \param chan Current channel pointer
+ * \retval NULL If the channel is a master channel or was not created by another.
+ * \return Channel pointer.  Refcounted, so the pointer MUST be discarded with ast_channel_unref.
+ */
+struct ast_channel *ast_channel_get_master(struct ast_channel *chan);
 #if defined(__cplusplus) || defined(c_plusplus)
 }
 #endif
Index: main/channel.c
===================================================================
--- main/channel.c	(revision 207316)
+++ main/channel.c	(working copy)
@@ -4361,10 +4361,22 @@
 	return __ast_request_and_dial(type, format, requestor, data, timeout, outstate, cidnum, cidname, NULL);
 }
 
+static void mchannel_free(void *data)
+{
+	struct ast_channel *mchan = data;
+	ast_channel_unref(mchan);
+}
+
+static struct ast_datastore_info mchan_info = {
+	.type = "MASTERCHANNEL",
+	.destroy = mchannel_free,
+};
+
 struct ast_channel *ast_request(const char *type, int format, const struct ast_channel *requestor, void *data, int *cause)
 {
 	struct chanlist *chan;
 	struct ast_channel *c;
+	struct ast_datastore *mchan_ds;
 	int capabilities;
 	int fmt;
 	int res;
@@ -4406,6 +4418,16 @@
 		if (!(c = chan->tech->requester(type, capabilities | videoformat | textformat, requestor, data, cause)))
 			return NULL;
 
+		/* Insert MASTERCHANNEL datastore */
+		if (requestor) {
+			if (!(mchan_ds = ast_datastore_alloc(&mchan_info, NULL))) {
+				ast_log(LOG_WARNING, "Master channel datastore allocation failed!\n");
+			} else {
+				mchan_ds->data = ast_channel_ref((struct ast_channel *) requestor);
+				ast_channel_datastore_add(c, mchan_ds);
+			}
+		}
+
 		/* no need to generate a Newchannel event here; it is done in the channel_alloc call */
 		return c;
 	}
@@ -7027,6 +7049,15 @@
 	return retval;
 }
 
+struct ast_channel *ast_channel_get_master(struct ast_channel *chan)
+{
+	struct ast_datastore *mchan_store = ast_channel_datastore_find(chan, &mchan_info, NULL);
+	if (mchan_store) {
+		return ast_channel_ref((struct ast_channel *) mchan_store->data);
+	}
+	return NULL;
+}
+
 /* DO NOT PUT ADDITIONAL FUNCTIONS BELOW THIS BOUNDARY
  *
  * ONLY FUNCTIONS FOR PROVIDING BACKWARDS ABI COMPATIBILITY BELONG HERE